Let's talk about what TDK does for clean energy

As society seeks ways to save energy and reduce its impact on the environment and climate, attention is turning to the means of power transmission needed to connect consumers to renewable energy sources such as offshore wind farms and remote solar power plants. After all, power losses over long distances can be significant. For this reason, power transmission system operators around the world are increasingly adopting VSC HVDC transmission systems that minimize these losses.

● How to stabilize voltage is a challenge faced by HVDC supporting offshore wind power generation

● Compact, large-capacity and long-life power capacitors play an important role in HVDC solutions.

How to stabilize voltage is a challenge facing HVDC supporting offshore wind power generation

The market size of HVDC (※1) systems will grow strongly in the coming years. The market size was just over US$7 billion in 2018, but is expected to increase by more than 60% to US$11.5 billion in 2025.

The main reason for the expected growth is not only the increase in electricity demand from electric vehicles and data centers, but also the growth of renewable energy. Since large wind farms and solar power plants are usually far away from the consumer population, they require transmission links with lower losses than traditional AC transmission technology (※2). The converters in these high-voltage direct current transmission systems (HVDC) provide a constant DC voltage and are therefore called voltage source converters (VSC).

Over long distances, VSC HVDC systems have much lower losses than AC transmission systems, which enables them to efficiently transmit power from remote power generation facilities via submarine cables and long-distance land links. VSC HVDC transmission technology (known as flexible direct current transmission in China) is particularly suitable for renewable energy sources such as offshore wind farms because its converter stations are compact enough to be easily installed on offshore platforms. In addition, the technology enables the interconnection of multiple subgrids with different voltages and is easier to control than AC systems. In addition, the VSC HVDC (flexible direct current transmission) system also has the advantage of reducing the cost of cable laying and other installation work.

A key challenge facing HVDC systems is achieving stable voltage. Voltage can easily become unstable during the transmission of power over long distances, creating the potential for problems such as damage to the distribution system and user equipment. Solving these problems requires power capacitors with high current capabilities that can withstand large voltage fluctuations. In addition, since such power capacitors are used in industrial power infrastructure and rail transportation applications, they also need to have high levels of durability and reliability.

The HVDC market is driven by the rising demand for electricity from electric vehicles and data centers and the increase in renewable energy.

The converter station is in the middle of the picture. Power capacitors are used here to stabilize the electricity.

Compact, high-capacity and long-life power capacitors play an important role in HVDC solutions.

TDK's power capacitors are key components in converter stations located at both ends of an HVDC link, converting AC power to DC current for transmission and then back to AC at the other end to feed the power back into the grid. In booster stations, which prepare power for long-distance transmission, capacitor banks are used to stabilize the DC voltage of the converters. In stations at the ends of an HVDC link, they ensure that the AC output voltage is suitable for feeding into the grid. As the use of renewable energy continues to grow around the world, these capacitors will also continue to help reduce transmission power losses and save energy.

In terms of technical characteristics, power capacitors using TDK's proprietary flat winding technology (※3) can achieve a volume fill factor of approximately 95% (※4). At the same time, the maximum capacitance of the capacitor exceeds 10,000μF (※5). This type of power capacitor has a very high current density and is compact in size (350×600×160mm). They are able to demonstrate excellent performance in the confined space of offshore converter stations and control voltage fluctuations. In addition, they have a self-healing function. Even if overvoltage causes an electrical failure inside the capacitor, the insulation layer will recover within a few microseconds to prevent short circuits. With the long-term stability of their temperature and electrical characteristics, they can provide an extremely reliable operating life of up to 40 years.

TDK capacitors have been installed in several HVDC projects in Europe, the United States, China, and elsewhere, and TDK has established a solid market position as a major supplier of power capacitors for HVDC systems, for example, in the HVDC project between Beijing and Zhangjiakou (Zhangjiakou is located about 250 kilometers northwest of the Chinese capital). The new grid was designed by the State Grid Corporation of China (SGCC), one of the world's leading power companies. It will play a key role in providing clean energy from remote wind, photovoltaic and hydropower for the 2022 Beijing Winter Olympics. The high-voltage direct current grid has the world's highest voltage level (550 kV) and the largest transmission capacity. Capacitors are key components of the converter station, which converts the AC current fed into each HVDC link at the beginning into DC current, preparing it for long-distance transmission. They are also installed in the converter station to convert the DC current back into AC at the other end.

The Zhangbei high-voltage direct current (HVDC) transmission network will integrate wind, solar, and hydropower resources far from residential areas into one transmission link to supply green electricity to Beijing.

The picture shows TDK's Malaga plant in Spain producing power capacitors for HVDC.

TDK's "MKK DCi-R model" power capacitor uses a patented flat coil method, which increases energy density by about 10% compared to previous models. The size is reduced to only 350mm×600mm×160mm.